# Parmenides

Philosophy I · Ancient Philosophy: From the Milesians to Plato · https://tryals.app/learn/philosophy-i/parmenides

## What Is, Is

Parmenides of Elea wrote a philosophical poem in which a goddess sets out two routes of inquiry, and the whole of subsequent Greek metaphysics is a response to it.

The **Way of Truth** starts from something apparently harmless: *what is, is; what is not, is not*. You cannot think or speak of what is not, because there is nothing there to think about. Since "nothing" cannot be an object of thought, any reasoning that requires it is illegitimate.

From this, Parmenides derives properties of **what-is** with genuine rigour:

| Property | Because |
|---|---|
| **Ungenerated** | Coming to be requires starting from what-is-not |
| **Imperishable** | Ceasing to be requires becoming what-is-not |
| **Indivisible** | Division requires gaps of what-is-not between parts |
| **Unchanging** | Change requires becoming what one is not |
| **Complete** | Lacking anything means lacking some being |

Each follows from refusing to let "what is not" do any work. Motion needs empty space to move into, but empty space is what-is-not, so there is none. Plurality needs boundaries separating things, but a boundary is where one thing is not, so there are none. What exists is **one, unchanging and whole**.

The **Way of Opinion** is the second part: the world as the senses report it, which the goddess presents while marking it as unreliable. Parmenides is thus the first thinker to hold that reason and the senses **systematically conflict**, and to side with reason without hesitation.

The conclusion is absurd and the argument is not obviously bad, which is exactly why it mattered so much. Nobody could simply dismiss it. Every subsequent Greek philosopher had to find the flaw or accept the consequence, and their responses are the next century of philosophy: the pluralists keep unchanging elements but let them mix, the atomists bite the bullet and admit void as a genuine kind of thing, and Plato distinguishes two levels of reality so that both Parmenides and Heraclitus can be partly right.

> **Common pitfall:** dismissing Parmenides because the conclusion is obviously false. That is not a refutation, an argument is refuted by finding the false premise or the invalid step, and nobody managed it for a very long time. The productive question is always *which* premise to reject, and Greek philosophy is largely a record of different answers.

## Practice questions

6 of this lesson's 11 practice questions, with answers. The full set is in the app.

### 1. Why does Parmenides conclude that motion is impossible?

A. Motion requires temporal succession, but what-is exists solely in a timeless present
B. Motion would require an external cause, yet nothing can exist outside of what-is
C. Motion is merely an illusion reported by the senses, which systematically deceive us
D. Motion requires empty space to move into, and empty space would be what-is-not

**Answer:** D. Motion requires empty space to move into, and empty space would be what-is-not

**Why:** Motion needs somewhere empty to move into, and emptiness is what-is-not, which cannot be. The unreliability of the senses is a separate strand, the argument against motion is purely a priori.

Page: https://tryals.app/practice/philosophy-i/parmenides/why-does-parmenides-conclude-that-motion-is-impossible

### 2. Parmenides insists that what is not cannot even be an object of thought. What follows from taking this constraint strictly when examining the apparent diversity of the physical world?

A. Sensory perception must be refined to observe genuine reality
B. The physical world ceases to exist whenever reason intervenes
C. Plurality is impossible because boundaries require non-being
D. Empty space exists as an underlying medium for material items

**Answer:** C. Plurality is impossible because boundaries require non-being

**Why:** Confusing the unreliability of perception with physical non-existence misreads the two ways; Parmenides denies the reality of division itself rather than offering an empirical fix. Admitting void concedes what-is-not, which later atomists embraced precisely to rescue motion.

Page: https://tryals.app/practice/philosophy-i/parmenides/parmenides-insists-that-what-is-not-cannot-even-be-an-object-of

### 3. Parmenides holds that where reason and the senses conflict, the senses should be trusted.

**Answer:** False

**Why:** False, he sides with **reason**, without hesitation. The Way of Opinion is the sensory world and the goddess marks it unreliable. That decision founds rationalism and shapes everything after him.

Page: https://tryals.app/practice/philosophy-i/parmenides/parmenides-holds-that-where-reason-and-the-senses-conflict-the

### 4. Which responses to Parmenides did later Greek thinkers actually make?

A. Keeping unchanging elements but allowing them to mix
B. Distinguishing two levels of reality so change belongs to one
C. Denying that his argument was valid in form
D. Admitting the void as a genuine kind of thing

**Answer:** A. Keeping unchanging elements but allowing them to mix; B. Distinguishing two levels of reality so change belongs to one; D. Admitting the void as a genuine kind of thing

**Why:** The pluralists, the atomists and Plato each rejected a different premise. Nobody succeeded in showing the argument formally invalid, which is exactly why it forced such radical metaphysical revisions.

Page: https://tryals.app/practice/philosophy-i/parmenides/which-responses-to-parmenides-did-later-greek-thinkers-actually-make

### 5. Arrange the steps of Parmenides’ central argument in order.

**Answer:**

1. There is nothing there for thought or speech to fasten onto
2. Any reasoning requiring what-is-not is therefore illegitimate
3. Coming to be, perishing, division and motion all require what-is-not
4. None of these is possible
5. What exists is one, unchanging and whole

**Why:** It begins as a claim about what can be *thought* and ends as a claim about what *is*. That transition, from the limits of thought to the structure of reality, is the move every later critic has had to examine.

Page: https://tryals.app/practice/philosophy-i/parmenides/arrange-the-steps-of-parmenides-central-argument-in-order

### 6. Sort each claim by whether Parmenides assigns it to the Way of Truth or the Way of Opinion.

**Answer:**

- Way of Truth: What is, is; what is not, is not, What exists is ungenerated and imperishable, Reality is one, indivisible and unchanging
- Way of Opinion: The world contains many things that move and change, The senses report a world of variety and becoming

**Why:** The division is between what reason proves and what the senses report, and Parmenides holds that where they conflict, reason wins. That is a genuinely radical commitment, and it is the origin of rationalism.

Page: https://tryals.app/practice/philosophy-i/parmenides/sort-each-claim-by-whether-parmenides-assigns-it-to-the-way-of-truth